"48 Hours" couldn't be a timelier pick-me-up for confirmed moviegoers. It guarantees a rich, amusing assortment of gratuitous kicks.

From "Hard Times" to "The Driver" to "The Warriors" to "The Long Riders" to "Southern Comfort," the gifted young writer-director Walter Hill has been evolving into an impressive and distinctive stylist, albeit with frequently motley or compromised story material. A delightful sort of dynamite entertainment, "48 Hours" ought to emerge as his first decisive commercial hit. A tense, exciting, profanely funny improvement on the fevered, weirdly reactionary urban police thrillers of the early '70s like "The French Connection" and "Dirty Harry," it also represents a sensational and probably style-setting update on the amiable interracial costarring chemistry that worked so well for Burt Lancaster and Ossie Davis in "The Scalphunters" and Sidney Poitier and Rod Steiger in "In the Heat of the Night."

On this auspicious occasion a highly explosive, uproarious chemistry is achieved by Nick Nolte, cast as a brawny, boozy, bad-tempered San Francisco homicide cop named Jack Cates (a hulking rambunctious caricature of Clint Eastwood's slow-burning Harry Callahan), and the young comedian Eddie Murphy, cast as a sleek, smart, sarcastic felon named Reggie Hammond. These verbally abusive, lovably disreputable heroes are drawn into a temporary, mutually satisfying and improving partnership when a trigger-happy member of Reggie's old gang (James Rembar as an extremely scary, powerful bad hombre named Ganz) escapes from a work detail in central California and turns up in San Francisco, leaving a trail of murder victims behind him, including two cops shot in an encounter that costs Jack Cates his trusty .44 and an immeasurable amount of manly and professional esteem.

Reluctantly, Jack agrees to spring Reggie from San Quentin for 48 hours in order to stake out the hideaways where Ganz might be expected to hide himself. The chase goes down to the wire, but by the time Jack and Reggie finally settle scores with their dangerous prey (in a brilliantly lit and orchestrated showdown sequence set in an alley of Chinatown, infernally illuminated by neon), they've also cemented the Beginning of a Beautiful Friendship.

Strictly speaking, the plot material is so trifling that it verges on the presumptuous. Instead of straining to conceal this defect by inventing plot complications, Hill finesses it by keeping the basic situation almost ridiculously simple and straightforward while supplying an abundance of enjoyable enhancements. Indeed, "48 Hours" illustrates how little substance you can get away with if the performers begin cooking together and most of the director's intuitions and skills pay off. It wouldn't be exaggerating much to say that the movie is all hyperbolic enhancement, a piece of cops-and-robbers nonsense transformed into a fresh, spontaneous genre gem by gratuitously enjoyable elements -- the fortuitous comic rapport of the costars, a convincing set of heavies, a distinctive pictorial style (a playful use of foreshortening and wide-angle lenses turns the principal setting into a curiously abstract San Francisco, as exotic and unfamiliar as the eerie San Francisco of "Petulia") and a rousing rock score (by the Busboys, generously showcased by Hill during a scene at a black nightclub).

While "48 Hours" is destined to send most satisfied customers out buzzing about Eddie Murphy's movie debut -- especially the Instant Classic sequence in which he buffaloes the clientele of a redneck bar (a rather implausible establishment for San Francisco, by the way) -- it ought to be apparent that he steals the movie with the indispensable sneaky connivance of Nolte and Hill. Indeed, the dazzle in Murphy's Reggie depends to a considerable extent on Nolte's generosity and evident lack of vanity, which permit him to portray Jack as an infuriating slob. In fact, Jack probably isn't so much a sendup of Dirty Harry as a transposed Archie Bunker. At any rate, Nolte seems to enjoy embodying this curt, decaying hulk, an insulting and roughneck white authority figure, humorously calculated to set up funny antagonistic responses and rejoinders from a wary, streetwise, quick-witted black companion.